DEVELOPMENTOF HIGH-EFFICIENCY DIRECT INJECTION DIESEL ENGINE BY CAVITATION INSIDE NOZZLE HOLE AND DISTURBANCE OF LIQUID FLOW

Diesel engine in internal combustion engine has the highest thermal efficiency and it leads to reduce carbon dioxide caused by global warming. However, it is demanded to reduce mainly nitrogen oxide NOx and soot emission in order to improve combustion efficiency and to progress thermal efficiency. Final objects of this study are to improve combustion efficiency and to reduce exhaust gas emission concentration by improvement of spray characteristics of injection nozzle for a direct injection Diesel engine. The author`s laboratory group has investigated that at first, it is to clarify dominant factor on atomization of liquid jet and spray, the second, it is to develop high-efficiency atomization enhancement nozzle, that is, development of the nozzle, which almost same spray characteristics at low-injection pressure is obtained ones of high-injection pressure in combustion of fuel spray. On previous researches including author`s studies, it was clarified that cavitation in the nozzle hole is dominant factor of atomization of liquid jet and spray. The author`s group has investigated about improvement of spray and flow characteristics of a direct injection Diesel nozzle by using cavitation phenomena and by changing only part of the nozzle hole. In usual, magnified-nozzle, for instance, 10 times magnified-acrylic nozzle is used to observe and to investigate mutual relationships between internal flow inside the nozzle hole and disintegration behavior of spray, because it is difficult to visualize clear cavitating flow inside the actual size nozzle hole. Therefore, it is necessary to observe and investigate about mutual relationships of internal flow in the nozzle hole and atomization of spray between magnified-nozzle and scaled-up nozzle for design high-efficiency atomization enhancement nozzle. Moreover, in case it thought about the matter in terms of energy saving and effective utilization of petroleum resources, effects of kinematic viscosity of liquid on internal flow in the nozzle hole and atomization of spray was studied. In general, although twin-fluid atomizer is used for atomization of high-viscosity liquid, possibility of atomization by using pressure atomized type nozzle like that a Diesel nozzle was studied from a point of view of energy saving. Moreover, direct injection Diesel nozzles are used a single hole nozzle and multi-hole nozzle with four or six hole numbers. In case Diesel nozzle, which is on the market, was used for engine, it has reported from some automobile makers that different spray characteristics, that is, mainly spread of sprays, spray tip penetration and droplet size distributions are different at each nozzle holes. This results lead to become worse spray characteristics and combustion characteristics, and then, it leads to affect exhaust gas characteristics. At that, the author`s group has designed that gathered multi-hole spray, which the same spray like that Diesel injection nozzle as sprays injected from actual multi-hole nozzle, has been obtained by dividing one nozzle hole into four nozzle holes. Furthermore, nozzles, which was dressed with round inlet cutting at inlet or outlet of the nozzle holes, and the nozzle, which inclined nozzle holes of multi-hole nozzle from vicinity of center of nozzle to outside of one, were used, authors have tried to improve dramatically spray characteristics and flow characteristics. Finally, when spread of intermittent spray of the nozzle with round inlet cutting at inlet of the nozzle hole becomes considerably large compared with the previous single hole nozzle under high-ambient pressure of Pa=1.6 MPa and ambient temperature of Ta=300 K; almost same conditions at just before top dead center of actual Diesel engine.